(1) Field of the Invention
The present invention relates generally to printing cellulosic articles and, more particularly, to a new and improved method of screen printing fabrics, in which the fabric article is first selectively printed with a chemical system including a dye blocking print paste and a dye enhancing print paste and subsequently dyed to bring out the print.
(2) Description of the Prior Art
Traditional screen printing of garments is done by printing ink, binder, thickener and softener combinations on dyed or white prepared for print (PFP) garments. A detailed description of the screen printing process is published in the Encyclopedia of Textiles, Second Edition, 1972 Prentice-Hall, Inc., Englewood Cliffs N.J., the disclosure of which is hereby incorporated by reference in its entirety. The following discussion is taken from the above-referenced Encyclopedia of Textiles.
The screen printing method in textiles is basically a stencil process. A wooden or metal frame is covered with a bolting cloth, which may be made of silk, fine metal thread, or nylon. The fabric is covered with a film and the design areas are cut out of the film just as in stencil making. The frame is then laid on the fabric and color is brushed or squeezed through the open areas of the film by the use of a big rubber knife or squeegee.
Originally, the design was cut out of film and then adhered to the screen. Today the cutting is done mechanically by a photo-chemical process which reproduces the design exactly as it was painted in the art which is being reproduced.
In printing, one screen is used for each color and these are accurately registered one on the other by the use of fixed stops attached to an iron rail running the length of the table. The length of the table determines the number of yards which can be printed at one laying; this varies depending on the available space, though 30 yards is considered the smallest space which is practical for economic production.
While screen printing, either by hand or machine, is a slower and more expensive process than roller printing, it has several virtues. From the point of view of design, pattern repeats can be much larger than in roller printing. Also, since the process is slower, pigment colors can be laid on in heavy layers to produce a handicraft effect. From an economic point of view, it does not require as large an investment as roller printing because the runs can be shorter, especially in the hand operation. This has encouraged smaller converters to adopt the screen method and to experiment more with design than they would be able to do in the roller method, where they would be required to contract for a minimum of about 8000 yards per pattern.
One of the most important physical parameters for good screen printing is that the print paste is thick enough to stand in a gel state until it is dried and cured. This assures clean crisp definition of the print.
However, the print paste still must flow readily and evenly. These two properties are defined as the rheology of the print paste and the most desirable property is called pseudo-plastic or the ability of the paste to become less viscous when moved by pump or mechanical device and to thicken or become more viscous when it stills.
Because of the nature of the print paste, screen prints are generally opaque and rubbery to the touch. In addition, these prints are not very durable especially when washed. There has been much work done in developing softer prints that do not crack and peel after washing and these softened prints are called "plastisols," but they are still based on pigments, binder, thickener and are still a surface coating which can be "felt".
Thus, there remains a need for a new and improved method of screen printing in which the garment or fabric may be printed using traditional screen printing techniques while, at the same time, provides printed areas which can not be rubbed off or felt to the touch.